1. Technical Field
The present disclosure relates to a toner for developing electrostatic latent images in the field of electrophotography, electrostatic recording, and electrostatic printing. The present disclosure also related to an image forming apparatus containing the toner.
2. Description of the Related Art
An electrophotographic full-color image forming apparatus generally forms an image with toner that comprises colored resin particles.
Recently, such full-color image forming apparatuses are widely used and required to produce images having much higher definition. To meet the requirement for higher-definition images, toner has been developed to be much more spherical and smaller. Thus, polymerization processes, which are generally capable of producing spherical and small toner, such as suspension polymerization, emulsion polymerization, and dispersion polymerization processes, are widely employed as toner production process recently in place of pulverization processes.
However, toner produced by a polymerization process (“polymerization toner”) has some drawbacks. One drawback is poor transfer efficiency due to its small size and large adhesive force. Another drawback is poor cleanability (i.e., removability from a photoreceptor) due to its spherical shape. Another drawback is that polymerization toner particles are likely to cause background fouling in resulting images because their surfaces are undesirably low in electric resistivity.
Electrophotographic developing processes are of two types: one-component developing process and two-component developing process. One-component developing process can be reliably performed with a simple and compact apparatus because a process of mixing toner and carrier particles is not needed, which meets a potential requirement for energy-saving and cost reduction. Thus, toner adaptable for one-component developing process is being developed recently.
In one-component developing process, toner particles get through a pressurized gap formed between a developing sleeve and a regulation blade so that the toner particles are charged. At the same time, however, the toner particles are undesirably stressed and degraded.
Moreover, the toner particles may undesirably adhere to the regulation blade or fuse on the developing sleeve without forming a desirable thin layer thereon.
On the other hand, for the purpose of saving energy, toner is required to be fixable at temperatures as low as possible. To meet this requirement, there has been an attempt to include a low-melting-temperature binder resin in toner. As usable low-melting-temperature binder resins, crystalline resins have been proposed that can rapidly melt upon application of heat. There has been another attempt to include a crystalline resin as a primary binder resin in toner.
Such toner having low-temperature fixability is also required to have heat-resistant storage stability. Heat-resistant storage stability may be improved by reforming toner surface by increasing the glass transition temperature thereof. However, merely increasing the glass transition temperature of toner surface would not prevent deformation of toner especially in a high-temperature and high-humidity condition, such as a case in which toner or toner cartridge is in transportation during which toner is generally exposed to a certain pressure. There have been attempts to increase the glass transition temperature and melting temperature of toner in whole.
JP-2010-77419-A describes a crystalline resin particle having specific melting and softening temperatures for improving heat resistance.
JP-2011-123483-A describes a toner having projections at surface of the toner. Each of the projections is formed of fine vinyl resin particles.
JP-2005-215298-A describes a toner having a core including a crystalline polyester and a shell layer including an amorphous polymer.